FMF - Friends of Minerals Forum, discussion and message board

[Oliver B]

Hardness test of 4 after my tests, That's why they are so interesting to me; I wonder why their structure changed, I concluded that it had to be Fluorite. Thanks bob!

[Oliver B]

Bob Harman,
I will post a few pictures of the geode I collected. I also thought it very strange to be in the river. I almost thought it was a discarded geode someone else collected or lost from another locale, however it wasn't cracked open yet.

[Bob Carnein]

Hi, again--can you tell me how you tested the hardness on the Alum Creek fluorites?

[Bob Harman]

OLIVER, Your last 3 photos almost certainly show a Mexican geode of the type I have pictured. These were marketed as Rock Candy Geodes at the 2007 Tucson show. They are quite similar to yours with starburst like groups of small sceptered quartz crystals. I have the example pictured in the poster.
Unless there are other very similar examples definitely associated with the Olentangy River Ohio locality, finding your example suggests it was discarded by someone in the past. Look around in that area again and maybe you will be lucky with additional finds!
BOB

[Oliver B]

Bob Carnein, I first tested the very tip of the crystal with my fingernail and it left visible scratches on my nail, following up I used a copper plated penny and found that it also scratched the copper. Finally I took a carbon steel knife and found that it scratched very easily on the fluorite. Combined with the fluorescence and the fact that the other crystals in the same rock dump were easily distinguishable as calcite with dog tooth spar formation, I drew the conclusion that it was Fluorite. I hope my hardness test was satisfactory.

[Chris Rayburn]

A very simple and definitive test--place a couple of drops of vinegar on it. If it fizzes, it's calcite; if not, it's fluorite or something else.

[Oliver B]

I will perform an acid test later today using vinegar. I have some pool based muriatic acid here that is around 30% concentration, on other samples to try and clean I mixed a 10:1 ratio of water and muriatic acid to remove calcite buildup and rust staining but what ended up happening was the crystals of fluorite in solution also began to loose their definitive edges and took on a glossy smooth appearance. I was under the impression that dilute HCL would not affect Fluorite crystals. Did i not dilute enough or would vinegar be the best solution? I have many nodules of pyrite from the area as well and wonder would the acid remove rust deposits?

[Tom Tucker]

I think the crystals in "the glossy area" are calcite that has been actively dissolved by the HCl. I don't see any fluorite. Tom

[Chris Rayburn]

Agree, looks like acid etched calcite. Dilute HCl and vinegar should have a similar effect on calcite, although dilute HCl will generally be more aggressive. HCl should have no effect on fluorite. I've had good luck cleaning pyrite nodules with HCl, but it depends largely on what type of material is coating the pyrite. It should not harm the pyrite in any event.

[Bob Harman]

If these are all the same examples that I originally commented on, then I was correct as they look like acid etched calcite. I therefore agree with Chris and Tom. BOB

[Oliver B]

these are separate examples. One of my apparent Fluorite specimens dissolved hard in dilute muriatic acid. It was a definite cube, which leads me to wonder if Fluorite cannot be dissolved by that solution or if calcite can grow in cubic crystal structure? the original rhombic shaped crystals are in fact fluorite, no fizz from vinegar, passed hardness tests. I will post more pictures now.

[Bob Harman]

In my opinion, all that you are showing are small crystals and cleavage portions of calcite. I see no fluorite! If your other example dissolved in dilute muriatic acid it also was calcite. That acid (28% HCl) specifically dissolves carbonates (including calcite) while having no effect on most non-carbonates including fluorite.

In addition.....and this can be important.....if all your specimens came from fill along a bike path along Alum Creek in Columbus Ohio, it would be statically much more likely to find pieces of calcite rather than fluorite. Calcite veins and small crystals are very common in nearby limestone, so pieces of calcite in your examples would be common while fluorite pieces would be comparatively quite uncommon making it unlikely that you found any.


OLIVER, since you seem to be enthusiastic, I suggest you join a local club and have the experienced club members help get you going. BOB

[Tom Tucker]

Your three newly posted photos show calcite only. Tom

[Jim Robison]

An important clue is the difference in shape between the two minerals. Fluorite is aa cubic mineral, which among other things mean the corners of natural crystals have a square shape or a variation on the same. Calcite is in a different crystal system, and has rhombohedral faces that are all inclined. In both minerals there are sets of parallel opposite faces, but in calcite they are inclined from the square. Fluorite always has some sets of parallel faces that are opposite but of a different orientation, but always based on the cubic oraientation. . You need to look at crystal shapes in pictures and at information on crystal shapes. I can't remember where on the Forum you find that, but believe there is a section on this topic.

As your collecting advances you will quickly discover that the form of a crystal, or a cleavage shape, is needed.

[Oliver B]

thanks all, there isnt much to find here in columbus and i havent found any clubs or organizations locally that i can join but ill keep learning the best i can!